1 Answer
1

In 64-bit mode, the operand size is fixed at 8+2 bytes. The instruction stores 8-byte base and 2-byte limit values.

and:

DEST[0:15] <- IDTR(Limit);
DEST[16:79] <- IDTR(Base);

This means your myData variable needs to be 10 bytes long, and the instructions stores the limit in the first 2 bytes and base address in the next 8 bytes. This also explains why your value matches with WinDbg's value after the first ffff bytes.